The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-348702 filed on Nov. 14, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a light-emitting device and an optical transmission unit for converting an electric signal into an optical signal and transmitting the optical signal.
2. Description of the Related Art
As a device for converting an electric signal into an optical signal, for example, a vertical-cavity surface-emitting laser diode (VCSEL) is in the actual use.
The VCSEL has the characteristics of small threshold current as compared with an end surface light-emitting laser diode and being easily put into an array.
Generally, the VCSEL has the features of low output as compared with a general laser diode and life shortened in proportion to the square or the cube of a current value if a drive current is increased.
For example, JP-A-7-38205 (Document 1) discloses a technique of generating an optical signal using a plurality of face light-emitting laser diodes.
However, in the technique disclosed in Document 1, a plurality of face light-emitting laser diodes each having a horizontal resonator, a waveguide, and a diffraction grating need to be disposed so that optical signals emitted from the face light-emitting laser diodes are gathered at one point, and it is hard to manufacture.
For example, JP-A-9-18423 (Document 2) discloses a laser diode array using a plurality of VCSELs for emitting different light wavelengths, a collimator array, and a condensing lens.
The laser diode array disclosed in Document 2 is used to transmit an optical signal by wavelength division multiplexing, and does not solve the problems of low output of VCSEL and shortening the life if the drive current is increased.
It is therefore an object of the invention to provide a light-emitting device capable of making up for the lowness of output of each vertical-cavity surface-emitting laser diode (VCSEL) and shortening of the life of the VCSEL if a drive current is increased and an optical transmission unit using the light-emitting device.
It is also an object of the invention to provide a light-emitting device of an array structure of a simple structure and an optical transmission unit using the light-emitting device.
[Light-emitting Device]
To the ends, according to the invention, there is provided a light-emitting device including a plurality of vertical-cavity surface-emitting laser diodes for emitting an optical signal in the same direction and a drive circuit for driving the plurality of vertical-cavity surface-emitting laser diodes by the same signal.
[Optical Transmission Unit]
According to the invention, there is provided an optical transmission unit including a light-emitting device and a light guide for receiving an optical signal emitted from the light-emitting device at one end and transmitting the optical signal to another end. The light-emitting device includes a plurality of vertical-cavity surface-emitting laser diodes for emitting optical signals in the same direction and a drive circuit for driving the plurality of vertical-cavity surface-emitting laser diodes by the same signal. The optical signals of the plurality of vertical-cavity surface-emitting laser diodes are transmitted through the light guide.
Preferably, the light-emitting device emits an optical signal to the one end of the light guide, which faces to an emission surface of the plurality of vertical-cavity surface-emitting laser diodes. Also, the plurality of vertical-cavity surface-emitting laser diodes are disposed in an area of the one end of the light guide.
Preferably, the plurality of vertical-cavity surface-emitting laser diodes are disposed like a grid.
Preferably, one of the plurality of vertical-cavity surface-emitting laser diodes is disposed like a coaxial.
Preferably, the light guide includes an optical dividing type light guide using a sheet-like light guide-for splitting the optical signal and a plurality of optical transmission lines for transmitting the split optical signals.